Extending Constructive Negation for Partial Functions in Lazy Functional-logic Languages

In this paper the mechanism of Default Rules for narrowing-based languages proposed in 24] is adapted to lazy narrowing. Every partial deenition of a function can be completed with a default rule. In a concrete function call, the default rule is applicable when the normal ones determine that they cannot compute the value of the call. Furthermore , when the goal has variables the evaluation mechanism provides constraints to the variables to make the default rule applicable. Lazy narrowing semantics are extended with the technique of constructive negation 4, 5, 27]. The main advantage is that the coroutining implementation technique described in 5], which is the basis for an eecient implementation, can be fully formalized in our framework.